Tracer Experiments Research Articles

Drivers of Phytoplankton Variability in and Near the Pearl River Estuary, South China Sea During Typhoon Hato (2017): A Numerical Study

AbstractThe Pearl River Estuary and adjacent seas in South China Sea are frequently affected by tropical cyclones (TCs). Previous in situ and remote sensing studies have found that typhoons can enhance phytoplankton biomass and induce blooms in this region. However, the mechanistic links between phytoplankton blooms and typhoons have not been well understood due to the interplay of multiple complex processes along the land‐ocean‐atmosphere interface. Here, we constructed an integrated modeling system with the marine ecosystem and sediment components for the China Great Bay Area. By using the integrated modeling system, we quantitatively investigated the phytoplankton response to hydrological conditions variations under Typhoon Hato (2017), a strong typhoon case. Passive tracer experiments showed that with high river discharge induced by heavy rainfall, the residence time within Lingding Bay is as short as 15 days, less than half of that under the climatological discharge. The increase in freshwater pulse washes out the phytoplankton biomass within Lingding Bay. While for the offshore region, the analysis of various source and sink terms for the offshore region's post‐typhoon response showed that the increase of phytoplankton biomass in the first week was because of the uplift of nutrient‐rich subsurface water, while in the second week, it was due to the seaward propagation of nearshore high phytoplankton biomass water. While riverine nutrients support phytoplankton growth in the third week, a large part of phytoplankton biomass was lost to zooplankton grazing, showing the system shifted from the bottom‐up control to the top‐down control.

The effect of air purifiers and curtains on aerosol dispersion and removal in multi-patient hospital rooms.

Airborne transmission of disease is of concern in many indoor spaces. Here, aerosol dispersion and removal in an unoccupied 4-bed hospital room were characterized using a transient aerosol tracer experiment for 38 experiments covering 4 configurations of air purifiers and 3 configurations of curtains. NaCl particle (mass mean aerodynamic diameter ~3 μm) concentrations were measured around the room following an aerosol release. Particle transport across the room was 1.5-4min which overlaps with the characteristic times for significant viral deactivation and gravitational settling of larger particles. Concentrations were close to spatially uniform except very near the source. Curtains resulted in a modest increase in delay and decay times, less so when combined with purifiers. The aerosol decay rate was in most cases higher than expected from the clean air delivery rate, but the reduction in steady-state concentrations resulting from air purifiers was less than suggested by the decay rates. Apparently, a substantial (and configuration-dependent) fraction of the aerosol is removed immediately, and this effect is not captured by the decay rate. Overall, the combination of curtains and purifiers is likely to reduce disease transmission in multi-patient hospital rooms.

Breast PET/MRI Hybrid Imaging and Targeted Tracers.

The recent introduction of hybrid positron emission tomography/magnetic resonance imaging (PET/MRI) as a promising imaging modality for breast cancer assessment has prompted fervent research activity on its clinical applications. The current knowledge regarding the possible clinical applications of hybrid PET/MRI is constantly evolving, thanks to the development and clinical availability of hybrid scanners, the development of new PET tracers and the rise of artificial intelligence (AI) techniques. In this state-of-the-art review on the use of hybrid breast PET/MRI, the most promising advanced MRI techniques (diffusion-weighted imaging, dynamic contrast-enhanced MRI, magnetic resonance spectroscopy, and chemical exchange saturation transfer) are discussed. Current and experimental PET tracers (18 F-FDG, 18 F-NaF, choline, 18 F-FES, 18 F-FES, 89 Zr-trastuzumab, choline derivatives, 18 F-FLT, and 68 Ga-FAPI-46) are described in order to provide an overview on their molecular mechanisms of action and corresponding clinical applications. New perspectives represented by the use of radiomics and AI techniques are discussed. Furthermore, the current strengths and limitations of hybrid PET/MRI in the real world are highlighted. EVIDENCE LEVEL: 2 TECHNICAL EFFICACY: Stage 2.

Rates and physicochemical drivers of microbial anabolic activity in deep-sea sediments and implications for deep time.

Sediment microorganisms influence global climate and redox by altering rates of organic carbon burial. However, the activity and ecology of benthic microorganisms are poorly characterized, especially in the deep sea. Here, we conducted nearly 300 stable isotope tracer experiments in sediments from the Pacific and Atlantic oceans (100-4500 m water depth) to determine the rates, spatial distribution, and physicochemical controls on microbial total anabolic activity, nitrogen fixation, and inorganic/organic carbon uptake. Using correlative and manipulative approaches, we find that total activity is limited primarily by organic carbon and/or energy. Activity correlates significantly with distance from shore, sediment depth, C:N ratios, and overlying chlorophyll concentrations and is stimulated by carbon but not nitrogen additions. Consistent with this, nitrogen fixation was undetected despite relatively low concentrations of porewater ammonium and the previous detection of nifH genes. Inorganic carbon uptake accounted for 7%-55% of carbon assimilation per sample (median 21%), suggesting chemoautotrophy is an important and unappreciated source of labile carbon in deep-sea sediments. Community 16S rRNA was dominated by Bacteria (<2% Archaea), primarily Desulfobacterales of the Deltaproteobacteria. Leveraging our findings, we modelled global benthic microbial activity through geologic time and find the potential for significant shifts in total activity with supercontinental cycles.

Uptake and Allocation of Newly Absorbed Nitrogen in Young Pear Trees Grafted onto Vigorous Rootstocks (Pyrus betulifolia)

Nitrogen is one of the essential elements for fruit tree growth. Therefore, a 15N tracing experiment was conducted to investigate the characteristics of nitrogen uptake and distribution in young pear trees. The experiment included: groups A and B, fertilized with 15 g unlabeled and 5 g labeled N per tree in the spring of 2017; and group C, fertilized with 20 g unlabeled N per tree in the spring of 2017 and 25 g unlabeled and 5 g labeled N per tree in the spring of 2018. Results indicated that new organs grew vigorously before June, and about 50% of the fertilizer nitrogen was concentrated in leaves. From June to November, the growth rate of storage organs was faster than that of new organs, and fertilizer nitrogen was mainly stored in the shoots, trunk, and roots. During the defoliation period, about 84% of the leaf fertilizer nitrogen was mobilized to the shoots, trunk, and roots. There was significant correlation between current fertilizer nitrogen and the dry mass weight of each organ after the completion of the nitrogen cycling of a whole year; the correlation coefficient was 0.98. Fertilizer nitrogen use efficiency increased with the ages of the pear trees. Therefore, nitrogen fertilizer rate should be formulated according to the tree growth characteristics and increased with the ages of the young pear trees; topdressing fertilizer should be applied in summer to ensure trunk and root development.

Identification and Characterization of a Cryptic Bifunctional Type I Diterpene Synthase Involved in Talaronoid Biosynthesis from a Marine-Derived Fungus.

We report the identification of the tnd biosynthetic cluster from the marine-derived fungus Aspergillus flavipes and the in vivo characterization of a cryptic type I diterpene synthase. The heterologous expression of the bifunctional terpene synthase led to the discovery of a diterpene backbone, talarodiene, harboring a benzo[a]cyclopenta[d]cyclooctane tricyclic fused ring system. The conversion of geranylgeranyl diphosphate to talarodiene was investigated using 13C-labeling studies, and stable isotope tracer experiments showed the biotransformation of talarodiene into talaronoid C.

An extended 3-compartment model for describing step change experiments in pharmaceutical twin-screw feeders at different refill regimes

Residence time distributions (RTDs) are a valuable tool for product tracking in the unit operations of a continuous line for manufacturing pharmaceutical oral solid dosage (OSD) and the integrated system itself. The first unit operation in such a continuous line in which extended intermixing can occur, is typically a feeder. The RTD of a feeder can be obtained by performing tracer experiments with a tracer material. A physical interpretation can be given to the observed tracer concentration responses by fitting a tanks-in-series (TIS) or compartmental model to it. Consequently, the internal mixing behaviour inside the feeder hopper can be rationalized. However, typically, a constant volume is assumed for the tanks or compartments in these models. This has led to several publications where the experimental set-up does not violate the constant volume assumption, i.e. one performs refills at a high hopper fill level. Here, we step away from this assumption and develop a set of differential equations for a 3-compartment model in order to account for a non-constant volume of the compartments. Moreover, the model distinguishes between a bypass trajectory formed by the agitator inside the feeder and an inner mixing volume, in which the tracer concentration lags on the tracer concentration in the bypass volume. This compartmentalization was inspired by the results obtained in a previous study using a spatial sampling method to assess the tracer concentration throughout the feeder hopper for different experimental runtimes. The developed model successfully describes the step responses for different refill regimes: the standard smooth first order plus dead time response (FOPDT) for a high refill regime and the more complex step response, including dips in the rising phase of the curve, for the low refill regime. As a consequence, a more thorough understanding of the complex mixing behaviour inside the feeder is obtained, which allows for an improved traceability. Next to that, the model delivers enhanced knowledge on the interaction between the residence time and the refill regime. The developed model was fitted to a data set, containing step change experiments for different pharmaceutical materials (Tablettose 80 (T80), Microcelac 100 (MCL), and Avicel PH101 (MCC)), different mass flow rates, and refill regimes. The experimentally observed phenomena could be reliably described by the proposed model. The model showed an improved transferability compared to typical TIS models.

Hepatic leukemia factor-expressing paraxial mesoderm cells contribute to the developing brain vasculature.

ABSTRACTRecent genetic lineage tracing studies reveal heterogeneous origins of vascular endothelial cells and pericytes in the developing brain vasculature, despite classical experimental evidence for a mesodermal origin. Here we provide evidence through a genetic lineage tracing experiment that cephalic paraxial mesodermal cells give rise to endothelial cells and pericytes in the developing mouse brain. We show that Hepatic leukemia factor (Hlf) is transiently expressed by cephalic paraxial mesenchyme at embryonic day (E) 8.0-9.0 and the genetically marked E8.0 Hlf-expressing cells mainly contribute to the developing brain vasculature. Interestingly, the genetically marked E10.5 Hlf-expressing cells, which have been previously reported to contain embryonic hematopoietic stem cells, fail to contribute to the vascular cells. Combined, our genetic lineage tracing data demonstrate that a transient expression of Hlf marks a cephalic paraxial mesenchyme contributing to the developing brain vasculature.This article has an associated First Person interview with the first author of the paper.

Elucidating mobilization mechanisms of uranium during recharge of river water to contaminated groundwater

The recharge of stream water below the baseflow water table can mobilize groundwater contaminants, particularly redox-sensitive and sorptive metals such as uranium. However, in-situ tracer experiments that simulate the recharge of stream water to uranium-contaminated groundwater are lacking, thus limiting the understanding of the potential mechanisms that control the mobility of uranium at the field scale. In this study, a field tracer test was conducted by injecting 100 gal (379 l) of oxic river water into a nearby suboxic and uranium-contaminated aquifer. The traced river water was monitored for 18 days in the single injection well and in the twelve surrounding observation wells. Mobilization of uranium from the solid to the aqueous phase was not observed during the tracer test despite its pre-test presence being confirmed on the aquifer sediments from lab-based acid leaching. However, strong evidence of oxidative immobilization of iron and manganese was observed during the tracer test and suggested that immobile uranium was likely in its oxidized state as U(VI) on the aquifer sediments; these observations ruled out oxidation of U(IV) to U(VI) as a potential mobilization mechanism. Therefore, desorption of U(VI) appeared to be the predominant potential mobilization mechanism, yet it was clearly not solely dependent on concentration as evident when considering that uranium-poor river water (<0.015 mg/L) was recharged to uranium-rich groundwater (≈1 mg/L). It was possible that uranium desorption was limited by the relatively higher pH and lower alkalinity of the river water as compared to the groundwater; both factors favor immobilization. However, it was likely that the immobile uranium was associated with a mineral phase, as opposed to a sorbed phase, thus desorption may not have been possible. The results of this field tracer study successfully ruled out two common mobilization mechanisms of uranium: (1) oxidative dissolution and (2) concentration-dependent desorption and ruled in the importance of advection, dispersion, and the mineral phase of uranium.

Root-Zone CO2 Concentration Affects Partitioning and Assimilation of Carbon in Oriental Melon Seedlings.

Root-zone CO2 is essential for plant growth and metabolism. However, the partitioning and assimilation processes of CO2 absorbed by roots remain unclear in various parts of the oriental melon. We investigated the time at which root-zone CO2 enters the oriental melon root system, and its distribution in different parts of the plant, using 13C stable isotopic tracer experiments, as well as the effects of high root-zone CO2 on leaf carbon assimilation-related enzyme activities and gene expressions under 0.2%, 0.5% and 1% root-zone CO2 concentrations. The results showed that oriental melon roots could absorb CO2 and transport it quickly to the stems and leaves. The distribution of 13C in roots, stems and leaves increased with an increase in the labeled root-zone CO2 concentration, and the δ13C values in roots, stems and leaves increased initially, and then decreased with an increase in feeding time, reaching a peak at 24 h after 13C isotope labeling. The total accumulation of 13C in plants under the 0.5% and 1% 13CO2 concentrations was lower than that in the 0.2% 13CO2 treatment. However, the distributional proportion of 13C in leaves under 0.5% and 1% 13CO2 was significantly higher than that under the 0.2% CO2 concentration. Photosynthetic carbon assimilation-related enzyme activities and gene expressions in the leaves of oriental melon seedlings were inhibited after 9 days of high root-zone CO2 treatment. According to these results, oriental melon plants’ carbon distribution was affected by long-term high root-zone CO2, and reduced the carbon assimilation ability of the leaves. These findings provide a basis for the further quantification of the contribution of root-zone CO2 to plant communities in natural field conditions.

Simulation of experimental synthetic DNA tracer transport through the vadose zone

Although multiple experimental studies have proven the use of free synthetic DNA as tracers in hydrological systems, their quantitative fate and transport, especially through the vadose zone, is still not well understood. Here we simulate the water flow and breakthrough of deuterium (D) and one free synthetic DNA tracer from a 10-day experiment conducted in a transient variably saturated 1m3 10° sloped lysimeter using the HYDRUS-2D software package. Recovery and breakthrough flux of D (97.78%) and the DNA tracer (1.05%) were captured well with the advection-dispersion equation (R2 = 0.949, NSE = 0.937) and the Schijven and Šimůnek two-site kinetic sorption model recommended for virus transport modeling (R2 = 0.824, NSE = 0.823), respectively. The degradation of the DNA tracer was very slow (estimated to be 10% in 10 days), because the “loamy sand” porous media in our lysimeter was freshly crushed basaltic tephra (i.e., crushed rocks) and the microbes and DNase that could potentially degrade DNA in regular soils were rare in our “loamy sand”. The timing of the concentration peaks and the HYDRUS-2D simulated temporal and spatial distribution of DNA in the lysimeter both revealed the role of the solid-water-air contact lines in mobilizing and carrying DNA tracer under the experimental variably saturated transient flow condition. The free DNA was nearly non-selectively transported through the porous media, and showed a slightly early breakthrough, possibly due to a slight effect of anion exclusion or size exclusion. Our results indicate that free DNA have the potential to trace vadose zone water flow and solute/contaminant transport, and to serve as surrogates to trace viral pathogen pollution in soil-water systems. To our knowledge, this study is the first to simulate transport mechanisms of free synthetic DNA tracers through real soil textured porous media under variably saturated transient flow condition.

Coastal aeolian sediment transport in an active bed surface layer: Tracer study and conceptual model

AbstractCoastal aeolian sediment transport is influenced by supply‐limiting factors caused by sediment sorting by grain size. Sorting processes can lead to coarsening of the bed surface and influence the formation of aeolian ripples. However, the influence sorting processes and bedforms might have on the magnitude of the transport is not fully understood. This study explores sorting processes and their influence on the magnitude and mode of aeolian transport by using sediment tracers. Sand was painted in different colors according to particle size and placed on a supratidal beach in Noordwijk, the Netherlands. Several experiments were conducted with varying wind speeds. Surface sampling and cameras tracked the sand color movement on the bed surface, and wind velocity was measured. The tracer experiments showed that ripples developed in moderate wind conditions. Once the ripples had formed, the supply of finer tracer grains in the downwind direction decreased over time, while the supply of coarser grains remained constant. A linear relationship between ripple migration speed and wind speed was found. For higher wind speeds, no ripples or differences in transport of grain size fractions were observed. Instead, alternating phases of erosion and deposition of the bed surface were observed, which could not be related to local variations in wind velocity. Based on these results and literature, a conceptual model was developed for an active bed surface layer with two transport regimes corresponding to moderate (I) and high (II) wind speeds. The conceptual model is intended to guide the selection of aeolian sediment transport models as a function of wind speed, bed characteristics, and upwind sediment supply. For Regime I, transport could be modeled using a linear relationship between sediment transport and wind speed and for Regime II using a third power relationship in combination with a process‐based model accounting for supply limitations.

Bone morphogenetic protein-9 maybe an important factor which improves insulin resistance in PCOS

Background Polycystic ovary syndrome (PCOS) is closely related to insulin resistance (IR). Bone morphogenetic protein-9 (BMP-9) plays an important role in maintaining glucose homeostasis, but an association between BMP-9 and PCOS has not been reported. Here, we report the changes in BMP-9 and the influence of this protein on IR in PCOS. Methods 57 PCOS patients were selected (among them 25 received interventional treatment with exenatide (EX) for 3 months, and 32 received no treatment). 22 normal control individuals and 30 IR patients were also recruited. We evaluated IR with the euglycaemic-hyperinsulinaemic clamp (EHC) technique. IR and the glucose metabolism rate were assessed by EHC and [3-3H]glucose tracer experiments. We determined the protein expression levels of BMP-9, p-AKT (protein kinase B) and androgen receptor in the ovaries and liver by Western blotting. Results We found that circulating BMP-9 levels were significantly decreased in PCOS with IR patients. Circulating BMP-9 levels and p-AKT levels were decreased in HFD and PCOS rats and increased after MF and EX treatment. The glucose infusion rate, glucose disappearance rate and suppression of hepatic glucose production decreased in the HFD and PCOS groups, the opposite results were found for HGP. AR protein expression levels increased in the HFD and PCOS groups and decreased in the MF and EX groups. Conclusions Our study results suggest that BMP-9 is an independent factor that influences IR in PCOS patients. The decrease in BMP-9 levels in the liver and ovaries may be involved in IR through the PI3K/AKT signaling pathway in PCOS rats.

Lactate is an epigenetic metabolite that drives survival in model systems of glioblastoma

Lactate accumulates to a significant amount in glioblastomas (GBMs), the most common primary malignant brain tumor with an unfavorable prognosis. However, it remains unclear whether lactate is metabolized by GBMs. Here, we demonstrated that lactate rescued patient-derived xenograft (PDX) GBM cells from nutrient-deprivation-mediated cell death. Transcriptome analysis, ATAC-seq, and ChIP-seq showed that lactate entertained a signature of oxidative energy metabolism. LC/MS analysis demonstrated that U-13C-lactate elicited substantial labeling of TCA-cycle metabolites, acetyl-CoA, and histone protein acetyl-residues in GBM cells. Lactate enhanced chromatin accessibility and histone acetylation in a manner dependent on oxidative energy metabolism and the ATP-citrate lyase (ACLY). Utilizing orthotopic PDX models of GBM, a combined tracer experiment unraveled that lactate carbons were substantially labeling the TCA-cycle metabolites. Finally, pharmacological blockage of oxidative energy metabolism extended overall survival in two orthotopic PDX models in mice. These results establish lactate metabolism as a novel druggable pathway for GBM.

Benthic Macrofauna Community Bioirrigation Potential (BIPc): Regional Map and Utility Validation for the South-Western Baltic Sea.

Benthic community bioirrigation potential (BIPc), an index developed to quantify the anticipated capacity of macrofauna to influence the solute exchange at the sediment-water interface, was calculated for the south-western Baltic Sea. This index can be regarded as an effect trait that is useful for predicting ecosystem processes impacted by animal burrow ventilation. The special feature, and presumably an advantage, of BIPc, compared to alternative recently developed benthic macrofauna-based bioirrigation indices, lies in its ability to distinguish the taxa-specific score values between diffusion- and advection-dominated sediment systems. The usefulness of the BIPc index was compared against the estimates of the well-established community bioturbation potential index (BPc). The BIPc index displayed a moderately but significantly stronger correlation with estimates of irrigation rates derived from tracer experiments. Using a random forest machine learning approach and a number of available relevant environmental predictor layers, we have modelled and mapped the spatial differences in this ecosystem functioning expression. The key species contributing to bioirrigation potential in the study area were identified. The interannual variation in BIPc was assessed on a small exemplary dataset. The scores required to calculate the index, that were assigned to 120 taxa dominating abundance and biomass in the region, are provided for reuse. The utility, temporal variability and uncertainty of the distribution estimate are discussed.

Testing microbial models with data from a 14C glucose tracer experiment

Most of the carbon (C) that enters the soil is broken down by the microbial community and either respired or stored in soil depending on the microbial allocation strategy. Changes in how the microbial community uses C can significantly affect soil C pool sizes, so new models have begun to explicitly represent microbial allocation. Most models use a parameter called carbon use efficiency (CUE) to represent microbial allocation, which partitions consumed C between respiration and growth. Here we compare a “Typical Microbial Model” with this representation of microbial allocation to two other models. One is the “Microbial Allocation Model” that represents CUE as an emergent property of the microbial community, explicitly modeling multiple processes involved in CUE. The second is the “Two-Pool Biomass Model” that similarly accounts for CUE as an emergent property but also represents the biomass using two C pools with different turnover times. We assessed the models’ relative ability to track a14C-glucose tracer pulse over three weeks through the extractable C pool, the microbial biomass, and respiration. We also used the 14C data to test how estimates of microbial CUE change during the incubation. Our results suggest that CUE estimates in soil are sensitive to incubation timing and are at no point stable. Isotopic data can best parameterize models when a time course of measurements is used. Our model comparison showed that the Two-Pool Biomass Model best fit our data. Using the Two-Pool Biomass model to represent microbial allocation is more biologically realistic and better matches the dynamics observed in our microbial C partitioning data. Mechanistic biogeochemical models should consider using a dynamic allocation scheme to represent CUE, rather than assuming a static value.

Analysis of Elemental Dynamics in Plants by Radioisotope Tracer Experiments —Good to See, Good to Measure !—

Analysis of Elemental Dynamics in Plants by Radioisotope Tracer Experiments —Good to See, Good to Measure !—

Cracks and root channels promote both static and dynamic vertical hydrological connectivity in the Yellow River Delta

Vertical hydrological connectivity generally related heterogeneity of soil water and nutrient and the sustainability of vegetation restoration. Both the static and dynamic connectivity of soil have been studied for years, the relationship between them remains unclear, especially for coastal wetlands that greatly influenced by hydrological processes. In this study, static connectivity was defined as water flow paths and quantified by dye tracer experiment, whereas dynamic connectivity refers to the process of water movement and solute transport and described by solute penetration. Relationships between them were analyzed through the nonlinear fitting. Results showed that: 1) static connectivity was construed mainly by cracks in the upper soil layer and by root channels in the deeper soil, and these macropores led to heterogeneous distribution of water and solutes; 2) dynamic connectivity differed between soil columns, and non-equilibrium flow characterized by high infiltration rate and concentration in the initial phase was observed in soil with cracks and root channels; and 3) the static connectivity had significant effects on water movement while had no effects on solute transport. Infiltration rate decreased as dye coverage, fractal dimension, and the number of water pathway logistically increases. These findings highlight the importance of cracks and root channels on vertical hydrological connectivity in soil of S. salsa community, and suggest linking the static structure of water flow paths with soil water dynamic and heterogeneity to understand soil functions.

Increased nitrogen use efficiency via amino acid remobilization from source to sink organs in Brassica napus

Nitrogen (N) is an essential plant growth nutrient whose coordinated distribution from source to sink organs is crucial for seed development and overall crop yield. We compared high and low N use efficiency (NUE) Brassica napus (rapeseed) genotypes. Metabonomics and transcriptomics revealed that leaf senescence induced by N deficiency promoted amino acid allocation from older to younger leaves in the high-NUE genotype at the vegetative growth stage. Efficient source to sink remobilization of amino acids elevated the numbers of branches and pods per plant under a N-deficiency treatment during the reproductive stage. A 15N tracer experiment confirmed that more amino acids were partitioned into seeds from the silique wall during the pod stage in the high-NUE genotype, owing mainly to variation in genes involved in organic N transport and metabolism. We suggest that the greater amino acid source-to-sink allocation efficiency during various growth stages in the high-NUE genotype resulted in higher yield and NUE under N deficiency. These findings support the hypothesis that strong amino acid remobilization in rapeseed leads to high yield, NUE, and harvest index.

Hydrologic Turnover Matters — Gross Gains and Losses of Six First‐Order Streams Across Contrasting Landscapes and Flow Regimes

AbstractGross gains and losses of stream water and the consequent hydrologic turnover may modify the composition of stream water and drive in‐stream ecological functioning. We evaluated over 500 breakthrough curves of conservative tracer additions to analyze the channel water balance resulting in gross gains and losses, net exchange, and hydrologic turnover. During the hydrological year 2019, seven tracer experiments had been carried out in six first‐order streams along 400 m study reaches. All streams are located in the Holtemme catchment (Central Germany) with three each dominated by forested and agricultural land use. Four of the six streams were characterized by net‐losing conditions. The overall median of gross exchange was five times higher than net exchange. On average, subsurface gains replaced 50% of the original stream water over less than one kilometer of stream length. We even observed cases where over 95% of the stream water turned over within 100 m. Gross exchange was relatively higher in forested than in agricultural streams. Patterns of exchange in the forested streams persisted spatially and were temporally independent of streamflow, whereas in the agricultural ones, variable spatial patterns and streamflow dependence occurred. Overall, moderate flow coincided with highest relative gross exchange. Our results support previous findings that in‐stream solute concentrations could heavily depend on location and magnitude of gains and losses. Gross exchange embodies a permanent but variable control of downstream solute concentrations interacting with the signal of biogeochemical activity. We highlight the importance to include reach‐scale hydrological processes in studies on nutrient spiraling.